Measurement of the compression isentrope for 6061-T6 aluminum to 185GPa and 46% volumetric strain using pulsed magnetic loading

The Z accelerator at Sandia National Laboratories was used to measure the compression isentrope of 6061-T6 aluminum to 185GPa. The isentropic compression experimental technique uses a rapidly increasing, planar magnetic field to simultaneously subject multiple planar aluminum samples of different thicknesses to a ramped magnetic stress load. This magnetic stress load causes a ramped compression wave to propagate in the aluminum. Motion histories at the rear surface of each aluminum sample are measured through a LiF window using laser velocity interferometry. Backward and forward integration of the one-dimensional equations of motion are used to analyze the data. Imposing the requirement that each motion history comes from the same magnetic stress load is sufficient to determine both the stress load and the stress-strain behavior of the aluminum. Because of shocks that grow in the LiF, the usual VISAR interferometer analysis was modified. The measured compression curve obtained on different aluminum samples for volumetric strains to 46% agrees to within about 2% of peak stress with an isentrope obtained from the often-used Mie-Grüneisen equation of state that was derived from previous Hugoniot data.